905 Area Code – Hamilton, Ontario: Location, Time Zone & History

Ontario's 905 went into service October 11, 1993, splitting off from area code 416 to cover the ring of suburban municipalities encircling Toronto known as the Golden Horseshoe; permissive dialing of the old 416 numbers in the new territory continued only until January 1, 1994. As the region grew, 905 became the base of an expanding overlay complex: area code 289 arrived June 9, 2001, area code 365 followed March 25, 2013 to relieve the same 905/289 territory, and area code 742 was added October 16, 2021 after the CRTC projected the existing codes would exhaust their central office codes by late 2022.

Hamilton is the plan area's primary city, though Mississauga is its largest, alongside Brampton, Burlington, Oakville, and St. Catharines. The area's economy spans advanced manufacturing and steel, logistics and distribution, financial services back-office operations, and Niagara's wine and agriculture industry, supported by a strong base of higher education and research institutions.

Locally, the municipalities served by the 905/289/365/742 complex are simply known as "the 905," a term used in everyday speech to contrast the suburbs with Toronto's own "the 416," and the region is frequently cited as a bellwether in Canadian federal and provincial elections.